Barnaby Joyce may not be biological father of expected baby

Barnaby Joyce may not be the father of the baby boy his partner Vikki Campion is expecting, with the Nationals MP saying it was "a grey area".

The former deputy prime minister said he would raise the baby as his own but is not sure he is the biological father, Fairfax is reporting.

He claims he was not asked whether the child was his before Ms Campion's pregnancy was revealed to the Australian public on the front cover of The Daily Telegraph, eventually resulting in his resignation from Cabinet, reports News.com.au.

However, emails reportedly show the paper did ask him this before publishing the story.

The 50-year-old said he physically apart from Ms Campion, 33, for most of the period when the baby would have been conceived.

Mr Joyce confirmed in December last year that he had separated from his wife after winning a by-election in his seat of New England, sparked when he realised he was a dual citizen.

Vikki Campion. Photo / News Corp Australia

His relationship with Ms Campion, a former staffer in his office was revealed in February and then sparked scrutiny of his travel expenses and also claims of past harassment. The controversy resulted in a sex ban on ministers sleeping with staff and a feud with Prime Minister Malcolm Turnbull.

The couple was seen walking through Canberra airport on Friday, the first time they've been pictured together since news broke they were expecting a baby.